2011 Hydra-Matic 6T40 (Mh8) and 6T45 (Mh7, Mhc) Fwd/Awd Six-Speed Automatic

2012 HYDRA-MATIC 6T30 (MH9) SIX-SPEED AUTOMATIC

Vehicle Applications  Chevrolet Sonic

Product Highlights  Advanced clutch-to-clutch shift operation  Tuned for quick launch feel and fuel-efficient cruising  Compact design  Adaptive shift controls  Hyper-elliptical torque converter saves space  Maximum engine torque rating of 129 lb.-ft. (175 Nm)

Overview Six-speed automatic transmissions are integral in GM’s initiative to offer vehicles with excellent fuel economy and the Hydra-Matic 6T30 transmission delivers on that promise. Designed for compact FWD applications, it is used exclusively on the all-new Chevrolet Sonic.

The 6T30 is part of GM’s family of technologically advanced, fuel-saving six-speed automatics. Shared traits between the versions – and other Hydra-Matic six-speeds – reduce complexity, size and mass, including clutch-to-clutch operation that enables the six-speed to be packaged into approximately the same space of a four-speed automatic. The transmission has an overall 6.00:1 gear ratio spread, which contributes to an excellent balance of performance and fuel economy.

Because of the wide ratio spread, first gear is a very high ratio, which provides brisk acceleration from a stop. Sixth gear, however, is an overdrive ratio, which keeps the engine revolutions lower for highway cruising, reducing engine friction losses and optimizing fuel economy. On-Axis Design Instead of “folding” the transmission around the end of a transversely mounted engine, which has been one of the dominant GM transaxle design conventions, the 6T30 contains all of the gearing on the engine crankshaft centerline. The advantages of this layout enables a shorter overall vehicle length, more interior room and lower powertrain height.

Clutch-to-Clutch Shift Operation Three planetary gearsets are used with three stationary clutches and two rotating clutches, which save space compared to freewheeling designs. Freewheeling mechanisms allow accurate timing between shifts, but also take up more space and add more components to the transmission. Through electronic controls, the clutch-to-clutch concept of the 6T30 delivers optimal shift timing.

Gear changes from second to sixth gear ratios are accomplished with a precise clutch- to-clutch action, where the clutch is engaged in one gear at exactly the same time it is released in another. The first-to-second upshift, however, is a freewheeling action, where the second gear clutch engages while the first gear one-way clutch spins freely. This allows a greater degree of smoothness at lower vehicle speeds.

Adaptive Shift Controls Adaptive shift controls include automatic grade braking, which commands the transmission to remain in a lower gear if the vehicle is decelerating or coasting on a downgrade. This takes advantage of engine braking to prevent unwanted acceleration. This reduces the number of brake applies for the driver to brake during a hill descent. The control module receives input that monitors brake pedal usage, vehicle acceleration rate, throttle position, and even whether a trailer is connected to the vehicle.

Space-Saving Hyper-Elliptical Torque Converter The torque converter in the 6T30 uses a single-plate lock-up clutch and features a “hyper-elliptical” oval cross-section shape. This design reduces the thickness of the torque converter, reducing the space it needs and keeping the overall width of the engine and transmission as narrow as possible for packaging advantages. The single- plate converter clutch uses GM’s electronically controlled capacity clutch (ECCC) technology to help reduce engine vibrations and ensure smooth operation.

IX Gear Pump A compact on-axis, fixed-displacement IX gear-type fluid pump provides hydraulic pressure for shifting and lubrication. The pump features an IX gear (Drive/Driven) with a machined crescent in the pocket to reduce internal leakage and optimizes hydraulic efficiency. The inlet jet nozzle feature in the IX gear-type pump provides increased pump suction velocity, which helps optimize noise and vibration characteristics.

Ground and Honed Gears To minimize gear noise, as well as vibration, the transmissions’ helical gears are ground and honed to ensure precise dimensions and tolerances. With closer tolerances, the gears are less prone to characteristic whining or humming, allowing the transmission to operate with exceptional quietness.

Unique Input Shaft Bushings The input shaft requires no machining for grooves to contain fluid seals, which allows the shaft to retain maximum strength for its size and minimize cost.

Maintenance The 6T30 is filled for life with DEXRON®-VI premium fluid, which does not require changing under normal use. It was developed to have a more consistent viscosity profile; more consistent shift performance in extreme conditions; and less degradation over time.

Transmission Control Module A 32-bit transmission control module (TCM) monitors transmission performance and compensates for normal wear in components such as clutch plates, so transmission performance remains consistent for the life of the transmission. The control module also “tests” the components of the transmission following assembly to optimize the interaction of the components. The TCM is mounted inside the transmission, where temperatures remain mostly constant compared to an external-mounted module. It is small in size, which helps minimize the overall size of the transmission. The transmission and module are assembled together, so no additional connections are necessary during vehicle assembly.

Transmission Control Module A 32-bit transmission control module (TCM) monitors transmission performance and compensates for normal wear in components such as clutch plates, so transmission performance remains consistent for the life of the transmission. The control module also “tests” the components of the transmission following assembly to optimize the interaction of the components.